For decades one of the major problems associated with toilet systems for vehicles, such as boats, recreational vehicles, and the like, has been the relatively rapid failure of flexible hoses associated with said systems as far as the transmission of noxious odors are concerned. The flexible, typically PVC, hose associated with these toilet systems are sometimes in contact with sewage, particularly in adverse environments (such as tropical climates) for extended periods of time. In many circumstances the hose can fail in as little as three to six months in actual use, and when it does fail the noxious odors that it transmits can make the vehicle essentially unusable until the hose is replaced (the hose typically cannot be purged once it has failed).
It is because of the very significant practical problem that exists with such hoses that SeaLand Technology, Inc. of Big Prairie, Ohio has developed a testing procedure for hoses made of various materials to--in an accelerated manner--see if they can be expected to have a long life in the field, e.g. so that essentially hoses never have to be replaced because of odor permeation and transmission but only if they fail mechanically or the toilet system itself is replaced.
The term "SeaLand Sanitation Hose Permeability Test" as used in the present specification and claims means the test such as described in U.S. Pat. No. 5,442,952 (the disclosure of which is hereby incorporated by reference herein) in which the hose is first treated by introducing methyl alcohol into the hose sample and allowing the alcohol to stand for a day or more. Then one introduces into the hose sample (sealed at its ends, and with a barrier around it) a combination of dimethyl sulfide, carbon disulfide, and dimethyl disulfide. The sample is kept at about room temperature (e.g. about 72.degree. F.) and the sealed area around the hose is sensed for carbon disulfide. When a level of about 3 ppm carbon disulfide is sensed in the sealed volume surrounding the hose then it is considered that the hose has failed.
While literally dozens of hoses have been tested utilizing the SeaLand Sanitation Hose Permeability Test, until the invention the only hose that had acceptable odor transmission-resistant characteristics was one recently available from Australian Global Services Inc. of Perrysville, Ohio under the trade name AVS96 Marine Sanitation Hose. Conventional flexible PVC hose for vehicle toilet systems, when tested using the SeaLand Sanitation Hose Permeability Test, typically experiences hose failure in about two days (even though in real life situations the quickest failures are typically about three to six months). While it is not known whether there is a linear relationship between the failure under the SeaLand Sanitation Hose Permeability Test conditions and real life conditions, it is desired that in order to be relatively sure that a hose will not fail (that is transmit odors, particularly carbon disulfide) over its normal expected life in real life situations, it should not fail the SeaLand Sanitation Hose Permeability Test for at last eight days, and preferably for at least 12 days or more.
The AVS96 hose typically will not fail the SeaLand Sanitation Hose Permeability Test for eight days or more. While the AVS96 hose is the first hose to be successful from the odor permeation standpoint, for marine toilet system applications, it is very expensive, and its odor transmission resistance is not ideal. The formulation of the AVS96 hose is maintained as a trade secret by its manufacturer. While the AVS96 hose has been evaluated to determine its chemical constituents, those constituents cannot be precisely determined by reverse engineering, but it is believed that they comprise PVC with a low molecular weight plasticizer and a nitrile high molecular weight plasticizer.
By aggressively employing the testing methods of U.S. Pat. No. 5,442,952 to existing hoses, and instituting intense development work for new hose materials, the flexible hose odor transmission failure problem for a vehicle toilet system that has existed for decades has finally been cost effectively, and with a large margin or error, solved. According to the present invention a new hose formulation has been developed which is of lower cost than the AVS96 hose, and does not fail the SeaLand Sanitation Hose Permeability Test for a longer time than the AVS96 hose; that is it does not fail the test for at least eight days, and typically does not fail for thirteen days or more. The construction according to the present invention uses ethylene-vinyl-acetate (EVA) copolymer as the high molecular weight plasticizer, that copolymer having very poor carbon disulfide solubility. While EVA is known as a plasticizer for PVC for some products such as pool liners, water bed envelopes, or the like, significant amounts of EVA have not been heretofore known in the construction of unreinforced flexible hose, particularly for sewage transmission purposes.
According to one aspect of the present invention a vehicle toilet system is provided comprising: A toilet and a sewage holding tank mounted in a vehicle. And, a flexible hose for carrying sewage and operatively connected to at least one of the toilet and tank. The flexible hose comprising polyvinyl chloride, low molecular weight plasticizer, stabilizer, lubricant, and sufficient EVA high molecular weight plasticizer (which has poor carbon disulfide solubility) so that the hose will not fail the SeaLand Sanitation Hose Permeability Test for at least thirteen days. According to the preferred embodiment of the present invention the high molecular weight plasticizer comprises at least 10% by weight EVA copolymer, and more preferably at least 30% by weight EVA copolymer. The hose typically also contains filler and pigment. For example the hose may comprise, or consist essentially of, by weight, about 40-55% PVC resin, about 30-40% ethylene-vinyl-acetate copolymer, about 2-30% low molecular weight plasticizer, about 1-20% filler, and about 0.5-5% each of stabilizer and pigment, and about 0.05-0.5% lubricant. Even more EVA may be utilized to provide an even higher resistance to odor permeability, however EVA is relatively expensive and more than 40% is not necessary in order to, as a practical matter, achieve the desired results according to the invention. However should the EVA polymer price significantly decrease, or should particularly adverse environmental conditions for use of the flexible develop, more EVA can be used.
According to another aspect of the present invention a flexible hose per se is provided which comprises: An unreinforced tubular body capable of bending to form a radius and comprising: at least about 40% by weight PVC resin; at least about 10% by weight ethylene-vinyl-acetate copolymer; and low molecular weight plasticizer. The hose typically comprises at least about 30% by weight EVA, and typically also contains stabilizer, lubricant, filler and pigment. For example flexible hose according to the invention may consist essentially of, by weight, about 40-55% PVC resin, about 30-40% ethylene-vinyl-acetate copolymer, about 2-30% low molecular weight plasticizer, about 1-20% filler, about 0.5-5% each of stabilizer, and pigment, and about 0.05-0.5% lubricant.
That is the hose according to the invention, may comprise, by weight, at least about 40% PVC resin, at least about 30% ethylene-vinyl-acetate copolymer, at least about 2% low molecular weight plasticizer, at least about 1% filler, at least about 0.5% stabilizer, and at least about 0.05% lubricant. The lower molecular weight plasticizer, filler, stabilizer, lubricant, and--if utilized--pigment, may comprise any suitable conventional materials for that purpose, literally dozens of each of which are available commercially. However in the preferred embodiment of the invention the low molecular weight plasticizer comprises Di-octyl phthalate, the filler comprises calcium carbonate, the stabilizer comprises barium zinc, and the lubricant comprises stearic acid. For example a hose may be provided wherein the low molecular weight plasticizer comprises about 5-10% Di-octyl phthalate, wherein the filler comprises about 5-15% calcium carbonate, wherein the stabilizer comprises about 1-2% barium zinc stabilizer, wherein the lubricant comprises about 0.1-0.2% stearic acid, and further comprising about 1-2% titanium dioxide pigment. For example the flexible hose may consist of PVC, at least 10% by weight EVA, about 5-10% low molecular weight plasticizer, about 5-15% filler, about 1-2% stabilizer, about 0.1-0.2% lubricant, and about 1-2% pigment.
According to another aspect of the present invention a method of operating a toilet system, including a toilet, a sewage holding tank, a flexible hose connecting at least some of the components of the system, or in a pumpout system, is provided. The method comprises the step of: (a) Connecting at least one of the toilet and holding tank to each other and/or to other components of the system, or in a pumpoiut system, using flexible hose comprising polyvinyl chloride, and an EVA high molecular weight plasticizer which has poor carbon disulfide solubility, so that the hose will not fail the SeaLand Sanitation Hose Permeability Test for at least eight days (e.g. preferably for at least 13 days). Step (a) is typically further practiced by utilizing the details of the flexible hose as described above.
It is the primary object of the present invention to provide a relatively low cost flexible hose which will not fail, in the sense of transmitting odors (particularly carbon disulfide), over its expected mechanical life in vehicle toilet systems. This and other objects of the invention will become clear from an inspection of the detailed description of the invention, and from the appended claims.